1. Field of the Invention
The present invention relates to a temperature sensor and a temperature sensor attaching structure.
2. Description of the Related Art
In the related art, as devices become thinner and smaller, there are an increasing number of cases where a thermistor element used as a temperature sensor is mounted on a flexible board. For example, Japanese Unexamined Patent Application Publication No. 2010-015914 discloses a configuration in which a thermistor element is arranged on a flexible board.
FIG. 23 is a cross-sectional view of a sensor unit 30 that detects the temperature of a power generating element disclosed in Japanese Unexamined Patent Application Publication No. 2010-015914. The sensor unit 30 has a flexible board 31, and a thermistor element (temperature information detecting element) 32 and signal lines 33 and 35 which are formed on the surface of the flexible board 31. The flexible board 31 is covered by protective films 36. That is, the flexible board 31 including the thermistor element 32 and the signal lines 33 and 35 is sandwiched by two sheet-like protective films 36, and the outer edge portions of the two protective films 36 are secured to each other.
The sensor unit according to Japanese Unexamined Patent Application Publication No. 2010-015914 mentioned above is formed by arranging a thin temperature information detecting element on the flexible board, and assembling the resulting structure into a unit, with a view to detecting the temperature of the power generating element with greater accuracy while limiting the stress load applied to the power generating element.
However, the characteristic feature of the sensor unit according to Japanese Unexamined Patent Application Publication No. 2010-015914 resides in that the temperature information detecting element is connected to a connecting portion where the thickness in the board thickness direction of the flexible board is partially reduced. This temperature information detecting element itself has no flexibility. Therefore, even if the temperature information detecting element is formed of a thin film, a crack develops in the temperature information detecting element itself when a load is applied to the temperature information detecting element. In this case, the temperature information detecting element no longer functions as a temperature sensor. Moreover, because the temperature information detecting element is received inside the flexible board, the temperature information detecting element does not directly contact a temperature detection object, resulting in poor heat conduction. Therefore, it is difficult to directly detect the heat of the detection object. The deterioration of detection accuracy becomes particularly pronounced in a case where the temperature detection object generates only a small amount of heat.
It is also conceivable to mount a commonly used chip component on the flexible board, for example. However, such the commonly used chip component, even that which is handled as a small-sized component, typically has a thickness of about 200 μm (so-called 0402 size), which is very large in comparison to the thickness of commonly used flexible boards which typically ranges from 80 μm to 100 μm. For this reason, when a pressure is applied from the upper surface, a crack forms in the chip component, making temperature detection impossible.